1. Field of the Invention
The present invention relates to an interchangeable lens detachably attachable to a camera body.
2. Description of the Related Art
Interchangeable lenses detachably attachable to lens-interchangeable camera bodies such as digital cameras are required to be reduced in diameter and in thickness in an optical axis direction, as well as the camera bodies. Moreover, in order to perform good image capturing for close distance objects, the interchangeable lenses are required to be improved in their close distance optical performance including in-focus performance for the close distance objects.
Such improvement of the close distance optical performance needs good correction of variation of aberrations such as spherical aberration, field curvature and comatic aberration. Japanese Patent Laid-Open No. 2008-046482 discloses a lens apparatus employing, in order to correct aberrations well, a floating system in which its image capturing optical system is divided into two or more lens groups and these lens groups are moved for focusing at mutually different speeds by mutually different distances.
Japanese Patent Laid-Open No. 2008-046482 further discloses a cam mechanism that is a driving mechanism to move the lens groups by the mutually different distances. In the cam mechanism, cam pins provided to the lens groups engage with a straight groove portion formed in a fixed barrel and cam groove portions formed for the respective lens groups in a cam ring. The cam groove portions have mutually different cam lift amounts for a same rotation amount of the cam ring. Rotation of the cam ring with respect to the fixed barrel causes the cam groove portions having such mutually different cam lift amounts to move the cam pins and thereby moves the lens groups in an optical axis direction by mutually different distances.
However, when the above-mentioned cam mechanism is used for the floating system, the cam pins are arranged far away from one another in the optical axis direction, so that a length in the optical axis direction of the cam ring provided with the cam groove portions with which the cam pins are engaged becomes long. Such a long length of the cam ring increases an entire length of the lens apparatus, which makes it impossible to reduce a thickness of the lens apparatus.
The thickness can be reduced by increasing a diameter of the cam ring to overlap areas in which the respective cam groove portions are formed in the optical axis direction as much as possible. However, the increase of the diameter of the cam ring increases a diameter of the lens apparatus.
Thus, use of the cam mechanism as a mechanism moving the lens groups in the floating system lens apparatus makes it difficult to satisfy the requirement of reduction in diameter and thickness of the lens apparatus.